Retrofitting pleated cartridge filters into pulse-jet dust collectors designed for filter bags (i.e., unpleated filter media) has been a common practice for over ten years. The primary benefit is the large increase in filtration surface area, allowing the dust collector to operate at a lower differential pressure. In some cases the intention is to increase the air handling capability of the dust collection system without making any physical changes to the collector besides replacing the filter elements.
Methods for attaching the pleated cartridges to a tube sheet have been developed for both top and bottom load systems. The top load systems are favored, particularly in larger dust collectors, because of the easier clean-side access for installation and removal.
One method of top load attachment is a molded polyurethane structure at the top of the cartridge. An elastomer structure is provided having a groove, corresponding to the thickness of the tube sheet, that can be snapped into a tube sheet hole after sliding the cartridge through and pushing downward until the groove snaps into the tube sheet.
This attachment method has several drawbacks. When the molded polyurethane structure is designed to fit tightly enough to provide a leak-free seal, the cartridges are difficult to install and remove. Also, there are slight variations in the tolerances of the tube sheet holes that can result in air leaks. Over time, the polyurethane sealing structures become hard and embrittled or may change in dimension due to changes in temperature and/or through chemical attack. Subsequent failure of the seals results in dust emissions and premature failure of the filter elements.
Another popular method of top load attachment utilizes a vertical collar that is force-fit through a snap band sleeve of fabric material, similar to the top removal support for dust collector bags described in U.S. Pat. No. 4,292,057 to Ulvestad et al. In the modification for pleated cartridge filters, the collar assembly is a separate part that must be attached to the cartridge. This is accomplished by incorporating two or three threaded studs in the top end cap of the cartridge. The collar assembly, which includes a venturi and handle, is placed over the studded end cap. A gasket is required between the collar assembly and the studded end cap. Nuts and lock-washers are used to secure them before installation in the collector.
This method forms a durable air-tight seal between the cartridge and the tube sheet. However, the need to use separate components significantly adds to the cost of this method of attachment. The separate collar, end cap with two or three threaded studs, gasket, associated hardware, and the labor required for assembly are considered overly complicated to employ and are believed to add needless time and effort to filter maintenance.
Accordingly, it is a primary purpose of the present invention to provide an improved filter cartridge attachment means.